1. Field of the Invention
The present invention relates to a power transmission system including a power synthesizing mechanism connected to an electric motor and a power generator.
2. Related Art
In the recent years, there has been proposed a hybrid vehicle, on which an engine for outputting a power by burning a fuel and an electric motor for outputting a power by feeding it with an electric power are mounted as a drive source of the vehicle. On the basis of various conditions, the hybrid vehicle is enabled to improve the fuel economy and to reduce the noise and the exhaust gas emission by controlling the drive/stop of the engine and the electric motor.
One example of the hybrid vehicle having a plurality of drive sources mounted thereon is disclosed in Japanese Patent Laid-Open No. 8-183347 (JPA8-183347). The disclosed hybrid vehicle is constructed to include an engine, a power generator, a planetary gear unit, an electric motor and a differential. The output shaft of the engine and the rotor of the power generator are arranged concentrically with each other, and the planetary gear unit is arranged between the engine and the power generator. The planetary gear unit is equipped with a sun gear connected to a rotor, a pinion gear meshing with the sun gear and a ring gear, and a carrier holding the pinion gear and connected to the output shaft of the engine.
To the ring gear, moreover, there is connected the output shaft, which is equipped with a first gear. In parallel with the output shaft of the engine, there is disposed a counter shaft, which is equipped with a third gear and a fourth gear. The third gear meshes with the first gear. To the rotor of the electric motor, on the other hand, there is connected a second gear, which meshes with the third gear. Moreover, the differential is equipped with a fifth gear, which meshes with the fourth gear.
In the hybrid vehicle disclosed, moreover, the power outputted from the engine and the power outputted from the electric motor are synthesized by the third gear, and the synthesized torque can be transmitted to the differential. Still moreover, the electric power, which is generated as the power generator is rotated, is stored in a battery.
In the above-mentioned Japanese Patent Laid-Open, the second gear and the third gear function as the speed change mechanism to change the rotating speed of the electric motor and to synthesize the power of the electric motor and the power of the engine, while being prepared for the case in which the demand for raising the output of the electric motor occurs. The necessity for such a speed change mechanism raises a problem that the power transmission system is enlarged in size.